As electronic apparatuses operate at higher frequencies, capacitors used in the electronic apparatuses are required to have lower impedance at higher frequencies. To meet this requirement, solid electrolytic capacitors employing conductive polymer having higher conductivity has been developed.
Solid electrolytic capacitors to be used around CPUs of personal computers are required to have a large capacitance and a small size, and further, to have a small equivalent series resistance (ESR) at high frequencies as well as a low equivalent series inductance (ESL) for preferable noise reduction and transient response properties.
FIG. 21A is a sectional view of a conventional solid electrolytic capacitor disclosed in Patent Document 1. FIG. 21B is a sectional view of capacitor 501 at along line 21B-21B shown in FIG. 21A. Solid electrolytic capacitor 501 includes stacked plural capacitor elements 111 having a plate shape. Each capacitor element 111 includes positive electrode body 112 made of aluminum foil as valve metal foil, and a dielectric oxide layer provided on a surface of positive electrode body 112. The surface of positive electrode body 112 is roughened. Resist 113 having an insulating property is provided on the dielectric oxide layer, and separates positive electrode body 112 into positive electrode section 114 and a negative electrode deck. A solid electrolytic layer made of conductive polymer is provided on the dielectric oxide layer at the negative electrode deck. A negative electrode layer including a carbon layer and a silver paste layer is provided on the solid electrolytic layer, thus providing negative electrode section 115. In capacitor elements 111 having a plate shape, positive electrode sections 114 and negative electrode sections 115 are arranged along a longitudinal direction of the capacitor element.
Positive common terminal 116 is connected to positive electrode sections 114 of capacitor elements 111, and includes flat section 116A and connector section 116B that is formed by bending upward both sides of flat section 116A. Positive electrode sections 114 of stacked capacitor elements 111 are mounted to flat section 116A. Connector section 116B is bent to cover plural capacitor elements 111. A tip of connector section 116B is welded to positive electrode section 114 with laser beam.
Negative common terminal 117 is connected to negative electrode sections 115 of capacitor elements 111, and it has flat section 117A having negative electrode sections 115 mounted thereto. Flat section 117A and negative electrode section 115 are bonded together with conductive adhesive 118A. Negative electrode sections 115 of plural capacitor elements 111 are bonded together with conductive adhesive 118B.
Insulating package resin 119 covers capacitor elements 111 integrally such that a portion of positive common terminal 116 and a portion of negative common terminal 117 are exposed outside. The portion of positive common terminal 116 and the portion of negative common terminal 117 exposed outside are bent along package resin 119 to the bottom of package resin 119 as to form positive terminal section 116D and negative terminal section 117B, respectively, thus providing surface-mounting solid electrolytic capacitor 501.
The tip of connector section 116B of positive common terminal 116 and positive electrode section 114 of capacitor element 111 of solid electrolytic capacitor 501 are irradiated with a laser beam simultaneously, so that connector section 116B can be welded stably to positive electrode section 114.
Conventional solid electrolytic capacitor 501 thus requires positive common terminal 116 and negative common terminal 117 in order to cover stacked capacitor elements 111 with package resin 119, so that the number of components and the number of processes increase, hence increasing cost and preventing the capacitor from having a small size. Further, the distance between positive terminal 116D and negative terminal 117B as well as connected sections thereof prevents the capacitor having a small ESR and a small ESL.
FIG. 22 is a sectional view of another conventional chip solid electrolytic capacitor 502 disclosed in Patent Document 2. Positive lead-wire 412 made of tantalum wire is embedded in capacitor element 411 which is formed by press-molding powder of tantalum metal, i.e. valve metal, to have a cylindrical column shape with a press-mold die. Reinforcing section 411A having a conical shape protruding from the outer periphery of capacitor element 411 to positive lead-wire 412. The press-molded tantalum metal powder is sintered to be a porous positive electrode body, and then, is anodized, thereby providing a dielectric oxide layer on the surface of the positive electrode body. A solid electrolytic layer made of conductive polymer is formed on the dielectric oxide layer. Then, negative electrode layer 413 made of carbon and silver paint is formed on the surface of the solid electrolytic layer.
Positive lead-terminal 414 is welded to positive lead-wire 412. Negative lead-terminal 415 is connected to negative electrode layer 413 with conductive adhesive 416. Insulating package resin 417 covers capacitor element 411 such that a part of positive lead-terminal 414 and a part of negative lead-terminal 415 are exposed from an outer surface of the resin. Those parts exposed from the surface are bent along package resin 417 from the sides to the bottom of package resin 417 to form external terminals 414A and 415A, thus providing surface-mounting chip solid electrolytic capacitor 502.
Conventional chip solid electrolytic capacitor 502 includes reinforcing section 411A having conical shape and protruding from the outer periphery of capacitor element 411 to positive lead-wire 412. When the positive electrode body is produced by press-molding, tantalum metal powder tends to flow into reinforcing section 411A, and increase a density of the tantalum metal powder locally within reinforcing section 411A and at the vicinity thereof. This structure holds positive lead-wire 412 more steadily, and increases resistance of wire 412 against external load applied to wire 412. This structure prevents the dielectric oxide layer from cracking and breaking, and allows reliable chip solid electrolytic capacitor 502 to be steadily manufactured.
Conventional chip solid electrolytic capacitor 502 includes capacitor element 411 including positive lead-wire 412 connected with positive lead-terminal 414, and negative electrode layer 413 of element 411 connected with negative lead-terminal 415 to form external terminals 414A and 415A. This structure increases the number of components of capacitor 502 and the number of processes, hence increasing its cost and preventing the capacitor from having a small size. The lengths of external terminals 414A and 415A as well as connected sections of the terminals prevent eth capacitor form having small ESR and ESL.    Patent Document 1: JP2003-289023A    Patent Document 2: JP2005-085779A